Carbon Nanotube Microfiber Actuators with Reduced Stress Relaxation

Assembling carbon nanotubes (CNTs) into robust macroscopic structures remains the main challenge to efficiently exploit their electromechanical properties in actuator applications. CNT-based actuators generally suffer from creep and stress relaxation due to poor interactions between the assembled CNTs. In order to overcome this limitation, a new class of porous single wall CNT microfiber electrodes is here proposed. The present fibers are produced by a wet spinning process and generate a mechanical stress when they are stimulated at low voltage (∼1 V) in a liquid electrolyte. The used fabrication process enables the inclusion of small amounts of chemically cross-linked polymer such as poly(vinyl alcohol) within the fibers. The presence of cross-linked polymer limits the sliding of nanotubes with respect to each other, without sacrificing the porosity and electrical conductivity of the fibers. As a result, stress relaxation is greatly reduced. The fibers generate a negative stress (propensity to expand) when a positive or negative voltage is applied. This behavior suggests that the intrinsic deformation of the CNTs is likely the dominant actuation mechanism, as opposed to ionic swelling, which was recently observed in yarns made of multiwall CNTs.